Warning: Shadow Copies for Shared Folders are not a replacement for backup

Shadow Copies for Shared Folders are a great feature that can give your users access to previous files in minutes, as opposed to hours or even days (as it is takes normally to reclaim a file from the tape in an corporate environment).

One word of caution though: Shadow Copies for Shared Folders (SCSF) are not a substitute for backup. The same remark applies to any other type of shadow copies created through the default shadow copy provider (volsnap.sys). So, in addition to enabling SCSF you also need to rely on the good old backup to make sure you don't lose any data.

The reason for this warning is that the shadow copies can go away during exceptional circumstances. This doesn't happen normally, but here are some exceptions: 1) You do not have enough free space on the Shadow Storage disk. If there is not enough free space to keep the differences between shadow copies, then old shadow copies are simply deleted to make room for the new ones. Before enabling Shadow Copies for Shared Folders, make sure that you have enough space. At the very minimum several hundred of megabytes, but several Gigabytes is probably recommended. You can also control the maximum percentage can be consumed by SCSF. You can use the VSSADMIN command or the "Shadow Copies" tab in explorer to configure this maximum percentage/space to be used, so SCSF won't eat all your free space. 2) Disk corruption (due to the underlying hardware). While this is very unlikely to happen, it can happen any time... Nobody is immune to that, including shadow copies, which usually will get deleted automatically when a disk corruption is detected. 3) In very rare situations, on high-end systems, shadow copies for shared folders might be lost due to very high I/O activity. This issue was experienced by very few customers, and addressed by the latest VSS cumulative hotfixes: KB 833167 and KB 887827. See their associated web pages for more details. If you ever experienced the issues described in these hotfixes, you need to call Microsoft PSS to get a download location. The phone call is free.

[update: Adding an observation: the fact that shadow copies can go away applies only to shadow copies created with the default shadow copy provider. If you use a third-party shadow copy provider (hardware shadow copies for example) then you might have different lifetime guarantees.]